Variable geometry turbocharger

ABSTRACT

A variable geometry turbocharger ( 100 ) includes a bearing housing ( 10 ) including a bearing-housing side support portion ( 40 ) configured to support a radially outer portion ( 38 ) of a nozzle mount ( 16 ) from a side opposite to a scroll flow passage ( 4 ) in an axial direction of a turbine rotor ( 2 ), and wherein at least one of the following condition (a) or (b) is satisfied: (a) the bearing-housing side support portion ( 40 ) includes at least one bearing-housing side recess portion ( 46 ) formed so as to be recessed in the axial direction so as not to be in contact with the radially outer portion ( 38 ); (b) the radially outer portion ( 38 ) of the nozzle mount ( 16 ) includes at least one nozzle-mount side recess portion ( 62 ) formed so as to be recessed in the axial direction so as not to be in contact with the bearing-housing side support portion ( 40 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.16/087,907, filed on Sep. 24, 2018, which is the National Phase of PCTInternational Application No. PCT/JP2016/059938, filed on Mar. 28, 2016,all of which are hereby expressly incorporated by reference into thepresent application.

TECHNICAL FIELD

The present disclosure relates to a variable geometry turbocharger.

BACKGROUND ART

A variable geometry turbocharger adjusts the flow of exhaust gas to aturbine rotor from a scroll flow passage inside a turbine housing tochange the flow velocity and the pressure of exhaust gas to turbineblades, so as to enhance the supercharging effect.

As shown in FIG. 13, a variable nozzle mechanism 012 normally includes anozzle vane 014 disposed in an exhaust gas flow passage 026 for guidingexhaust gas from a scroll flow passage 004 to a turbine rotor 002, anozzle mount 016 having an annular shape and forming a flow passage wall028 on the side of a bearing housing 010, of the exhaust gas flowpassage, the nozzle mount 016 supporting the nozzle vane rotatably, anda nozzle plate 018 disposed so as to face the nozzle mount, the nozzleplate 018 having an annular shape and forming a flow passage wall 032opposite to the bearing housing, of the exhaust gas flow passage.

In the variable geometry turbocharger disclosed in Patent Document 1,the bearing housing includes a bearing-housing side support portionwhich supports the radially outer portion of the nozzle mount from theopposite side to the scroll flow passage in the axial direction of theturbine rotor, and the turbine housing includes a turbine-housing sidesupport portion which supports the radially outer portion of the nozzlemount from the opposite side to the bearing-housing side support portionin the axial direction. The nozzle mount is nipped by theturbine-housing side support portion and the bearing-housing sidesupport portion.

CITATION LIST Patent Literature

Patent Document 1: JP2013-72404A

SUMMARY Problems to be Solved

According to findings of the present inventors, in a case where thebearing housing includes the bearing-housing side support portionsupporting the radially outer portion of the nozzle mount like thevariable geometry turbocharger disclosed in Patent Document 1, asindicated by the arrow H in FIG. 13, the radially outer portion 038 ofthe nozzle mount 016 heated by the exhaust gas flow from the scroll flowpassage 004 releases heat toward the bearing-housing side supportportion 040, and heat loss occurs. The bearing housing is cooled bylubricant oil supplied to the bearing and has a lower temperature thanthe nozzle mount. Thus, a great heat loss tends to occur due to theabove heat release.

When heat loss occurs, the turbine thermal efficiency decreases, and theperformance of the variable geometry turbocharger also decreases.

Further, when heat loss occurs, the exhaust gas temperature of theturbine outlet decreases. Thus, in a case where a catalyst for purifyingexhaust gas is disposed on the downstream side of the turbine, thetemperature of the catalyst decreases and the performance of thecatalyst deteriorates, causing contamination of exhaust gas withimpurity substances (e.g. NOx and SOx).

The present invention was made in view of the above described typicalproblem, and an object is to provide a variable geometry turbochargercapable of reducing heat loss due to heat release from the radiallyouter portion of the nozzle mount to the bearing-housing side supportportion.

Solution to the Problems

(1) According to at least one embodiment of the present invention, avariable geometry turbocharger includes: a turbine rotor: a turbinehousing which accommodates the turbine rotor and which forms a scrollflow passage on a radially outer side of the turbine rotor: a bearinghousing accommodating a bearing which rotatably supports the turbinerotor, the bearing housing being coupled to the turbine housing: and avariable nozzle mechanism for adjusting a flow of exhaust gas to theturbine rotor from the scroll flow passage. The variable nozzlemechanism includes: a nozzle vane disposed in an exhaust gas flowpassage for guiding the exhaust gas from the scroll flow passage to theturbine rotor; a nozzle mount having an annular shape and supporting thenozzle vane rotatably, the nozzle mount forming a flow passage wall on abearing-housing side of the exhaust gas flow passage; and a nozzle platehaving an annular shape and being disposed so as to face the nozzlemount, the nozzle plate forming a flow passage wall on a side oppositeto the bearing housing, of the exhaust gas flow passage. The bearinghousing includes a bearing-housing side support portion configured tosupport a radially outer portion of the nozzle mount from a sideopposite to the scroll flow passage in an axial direction of the turbinerotor. At least one of the following condition (a) or (b) is satisfied:(a) the bearing-housing side support portion includes at least onebearing-housing side recess portion formed so as to be recessed toward aside opposite to the nozzle mount in the axial direction, (b) theradially outer portion of the nozzle mount includes at least onenozzle-mount side recess portion formed so as to be recessed to a sideopposite to the bearing housing in the axial direction.

According to the above variable geometry turbocharger (1), if thecondition (a) is satisfied, with the bearing-housing side recessportion, it is possible to reduce the contact area between thebearing-housing side support portion and the radially outer portion ofthe nozzle mount, and to reduce heat release amount from the radiallyouter portion of the nozzle mount to the bearing housing, through theheat insulating effect of the air layer between the bearing-housing siderecess portion and the radially outer portion of the nozzle mount.Accordingly, it is possible to reduce heat loss due to heat release fromthe radially outer portion of the nozzle mount to the bearing housing,and improve the turbine efficiency and the performance of theturbocharger.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

Furthermore, if the condition (b) is satisfied, with the nozzle-mountside recess portion, it is possible to reduce the contact area betweenthe bearing-housing side support portion and the radially outer portionof the nozzle mount, and to reduce the heat release amount from theradially outer portion of the nozzle mount to the bearing housing,through the heat insulating effect of the air layer inside thenozzle-mount side recess portion. Accordingly, it is possible to reduceheat loss due to heat release from the radially outer portion of thenozzle mount to the bearing housing, and improve the turbine efficiencyand the performance of the turbocharger.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

(2) In some embodiments, in the above variable geometry turbocharger(1), the at least one bearing-housing side recess portion or the atleast one nozzle-mount side recess portion includes a plurality ofbearing-housing side recess portions disposed at intervals in acircumferential direction of the turbine rotor or a plurality ofnozzle-mount side recess portions disposed at intervals in thecircumferential direction.

According to the above variable geometry turbocharger (2), with theplurality of bearing-housing side recess portions or the plurality ofnozzle-mount side recess portions provided at intervals in thecircumferential direction, it is possible to reduce the contact areabetween the bearing-housing side support portion and the radially outerportion of the nozzle mount effectively, and reduce the heat releaseamount from the radially outer portion of the nozzle mount to thebearing housing effectively, through the heat insulating effect of theair layer inside the nozzle-mount side recess portions.

(3) In some embodiments, the above variable geometry turbocharger (1) or(2) further includes a plurality of bolts disposed at intervals in acircumferential direction of the turbine rotor and configured to fastenthe turbine housing and the bearing housing in the axial direction. Thebearing-housing side recess portion or the nozzle-mount side recessportion is formed in an angular range which does not overlap with acenter position of a bolt adjacent to the bearing-housing side recessportion or the nozzle-mount side recess portion, of the plurality ofbolts, in the circumferential direction.

According to the above variable geometry turbocharger (3), for thebearing-housing side recess portion or the nozzle-mount side recessportion is formed in an angular range that does not overlap with thecenter position of an adjacent bolt in the circumferential direction, itis possible to reduce heat loss due to heat release from the radiallyouter portion of the nozzle mount to the bearing housing while ensuringa fastening force between the bearing housing and the turbine housingachieved by the bolt.

(4) In some embodiments, in the above variable geometry turbocharger(3), the bearing-housing side recess portion or the nozzle-mount siderecess portion is formed to be 5 degrees or more apart from the centerposition of the bolt adjacent to the bearing-housing side recess portionor the nozzle-mount side recess portion, of the plurality of bolts, inthe circumferential direction.

According to the above variable geometry turbocharger (4), for thebearing-housing side recess portion or the nozzle-mount side recessportion is formed to be 5 degrees or more apart from the center positionof the bolt, it is possible to reduce heat loss due to heat release fromthe radially outer portion of the nozzle mount to the bearing housingwhile ensuring a fastening force between the bearing housing and theturbine housing achieved by the bolts.

(5) In some embodiments, in the variable geometry turbocharger accordingto any one of the above (1) to (4), the turbine housing includes aturbine-housing side support portion configured to support the radiallyouter portion of the nozzle mount from a side opposite to thebearing-housing side support portion in the axial direction. The nozzlemount is nipped by the turbine-housing side support portion and thebearing-housing side support portion. The turbine-housing side supportportion is disposed so as to protrude toward an inner side of thebearing-housing side support portion in a radial direction of theturbine rotor, along a surface of the nozzle mount.

Typically, to nip the nozzle mount with a simple structure, the radiallyinner end of the turbine-housing side support portion is positioned onthe same position as the radially inner end of the bearing-housing sidesupport portion with respect to the radial direction.

In contrast, according to the above variable geometry turbocharger (5),the turbine-housing side support portion is disposed so as to protrudetoward the inner side, with respect to the radial direction, of thebearing-housing side support portion along the surface of the nozzlemount, and accordingly, the area of the nozzle mount covered with theturbine-housing side support portion is larger than that in a typicalstructure (normal design range). Thus, it is possible to reduce the areaof a portion of the nozzle mount exposed to a high-temperature exhaustgas flow from the scroll flow passage to the exhaust gas flow passage(heat transfer area). Accordingly, the heat absorption amount of thenozzle mount reduces, and thus an increase in the metal temperature ofthe nozzle mount is suppressed. Accordingly, the temperature differencebetween the nozzle mount and the bearing housing becomes small, and thusit is possible to reduce heat loss due to heat release from the radiallyouter portion of the nozzle mount to the bearing housing, and improvethe turbine efficiency and the performance of the turbocharger.

(6) According to at least one embodiment of the present invention, avariable geometry turbocharger includes: a turbine rotor; a turbinehousing which accommodates the turbine rotor and which forms at least apart of a scroll flow passage through which exhaust gas to be suppliedto the turbine rotor flows; a bearing housing accommodating a bearingwhich rotatably supports the turbine rotor, the bearing housing beingcoupled to the turbine housing; and a variable nozzle mechanism foradjusting a flow of exhaust gas to the turbine rotor from the scrollflow passage formed on a radially outer side of the turbine rotor. Thevariable nozzle mechanism includes: a nozzle vane disposed in an exhaustgas flow passage for guiding the exhaust gas from the scroll flowpassage to the turbine rotor; a nozzle mount having an annular shape andsupporting the nozzle vane rotatably, the nozzle mount forming a flowpassage wall on a bearing-housing side of the exhaust gas flow passage;and a nozzle plate having an annular shape and being disposed so as toface the nozzle mount, the nozzle plate forming a flow passage wall on aside opposite to the bearing housing, of the exhaust gas flow passage.The bearing housing includes a bearing-housing side support portionconfigured to support a radially outer portion of the nozzle mount froma side opposite to the scroll flow passage in an axial direction of theturbine rotor. The turbine housing includes a turbine-housing sidesupport portion configured to support the radially outer portion of thenozzle mount from a side opposite to the bearing-housing side supportportion in the axial direction. The nozzle mount is nipped by theturbine-housing side support portion and the bearing-housing sidesupport portion. The turbine-housing side support portion is disposed soas to protrude toward an inner side of the bearing-housing side supportportion in a radial direction of the turbine rotor, along a surface ofthe nozzle mount.

Typically, to nip the nozzle mount with a simple structure, the radiallyinner end of the turbine-housing side support portion is positioned onthe same position as the radially inner end of the bearing-housing sidesupport portion with respect to the radial direction.

In contrast, according to the above variable geometry turbocharger (6),the turbine-housing side support portion is disposed so as to protrudetoward the inner side, with respect to the radial direction, of thebearing-housing side support portion along the surface of the nozzlemount, and accordingly, the area of the nozzle mount covered with theturbine-housing side support portion is larger than that in a typicalstructure (normal design range). Thus, it is possible to reduce the areaof a portion of the nozzle mount exposed to a high-temperature exhaustgas flow from the scroll flow passage to the exhaust gas flow passage(heat transfer area). Accordingly, the heat absorption amount of thenozzle mount reduces, and thus an increase in the metal temperature ofthe nozzle mount is suppressed. Accordingly, the temperature differencebetween the nozzle mount and the bearing housing becomes small, and thusit is possible to reduce heat loss due to heat release from the radiallyouter portion of the nozzle mount to the bearing housing, and improvethe turbine efficiency and the performance of the turbocharger.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

(7) In some embodiments, in the above variable geometry turbocharger (5)or (6), the turbine-housing side support portion includes a contactportion to be in contact with the radially outer portion of the nozzlemount, and a non-contact portion formed on an inner side of the contactportion in the radial direction, the non-contact portion facing thenozzle mount via a gap.

With the above configuration (7), the turbine-housing side supportportion has the non-contact portion on the inner side of the contactportion with respect to the radial direction, and thus it is possible tocover the radially outer portion of the nozzle mount with theturbine-housing side support portion while suppressing an increase inthe contact area between the bearing-housing side support portion andthe radially outer portion of the nozzle mount. Accordingly, it ispossible to reduce the area of a portion of the nozzle mount exposed toa high-temperature exhaust gas flow from the scroll flow passage to theexhaust gas flow passage (heat transfer area), and suppress an increasein the heat input amount to the radially outer portion of the nozzlemount from the turbine-housing side support portion. Accordingly, it ispossible to suppress an increase in the metal temperature of the nozzlemount effectively, and reduce heat loss due to heat release from theradially outer portion of the nozzle mount to the bearing housingeffectively.

(8) In some embodiments, in the variable geometry turbocharger accordingto any one of the above (5) to (7), an expression 0≤(r1−r3)/(r2−r3)≤0.75is satisfied, where r1 is a distance between a radially inner end of theturbine-housing side support portion and a rotational axis of theturbine rotor, r2 is a distance between a radially outer end of thenozzle mount and the rotational axis, and r3 is a distance between aradially outer end of the nozzle plate and the rotational axis.

According to the above variable geometry turbocharger (8), it ispossible to suppress an increase in the metal temperature of the nozzlemount effectively while suppressing interference by the turbine-housingside support portion to a smooth flow in the exhaust gas flow passagebetween the nozzle mount and the nozzle plate, and reduce heat loss dueto heat release from the radially outer portion of the nozzle mount tothe bearing housing effectively.

(9) In some embodiments, in the above variable geometry turbocharger(8), an expression 0≤(r1−r3)/(r2−r3)≤0.30 is satisfied.

According to the above variable geometry turbocharger (9), it ispossible to suppress an increase in the metal temperature of the nozzlemount effectively while suppressing interference by the turbine-bearingside support portion to a smooth flow in the exhaust gas flow passagebetween the nozzle mount and the nozzle plate, and reduce heat loss dueto heat release from the radially outer portion of the nozzle mount tothe bearing housing effectively.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

(10) In some embodiments, the variable geometry turbocharger accordingto any one of the above (1) to (9) further includes a heat shield memberdisposed between the bearing-housing side support portion and the nozzlemount.

According to the above variable geometry turbocharger (10), through theheat shield effect of the heat shield member, it is possible to reducethe heat release amount from the radially outer portion of the nozzlemount to the bearing housing. Accordingly, it is possible to reduce heatloss due to heat release from the radially outer portion of the nozzlemount to the bearing housing, and improve the turbine efficiency and theperformance of the turbocharger.

(11) According to at least one embodiment of the present invention, avariable geometry turbocharger includes: a turbine rotor; a turbinehousing which accommodates the turbine rotor and which forms at least apart of a scroll flow passage through which exhaust gas to be suppliedto the turbine rotor flows; a bearing housing accommodating a bearingwhich rotatably supports the turbine rotor, the bearing housing beingcoupled to the turbine housing; and a variable nozzle mechanism foradjusting a flow of exhaust gas to the turbine rotor from the scrollflow passage formed on a radially outer side of the turbine rotor. Thevariable nozzle mechanism includes: a nozzle vane disposed in an exhaustgas flow passage for guiding the exhaust gas from the scroll flowpassage to the turbine rotor; a nozzle mount having an annular shape andsupporting the nozzle vane rotatably, the nozzle mount forming a flowpassage wall on a bearing-housing side of the exhaust gas flow passage;and a nozzle plate having an annular shape and being disposed so as toface the nozzle mount, the nozzle plate forming a flow passage wall on aside opposite to the bearing housing, of the exhaust gas flow passage.The bearing housing includes a bearing-housing side support portionconfigured to support a radially outer portion of the nozzle mount froma side opposite to the scroll flow passage in an axial direction of theturbine rotor. A heat shield member is disposed between thebearing-housing side support portion and the nozzle mount.

According to the above variable geometry turbocharger (11), through theheat shield effect of the heat shield member, it is possible to reducethe heat release amount from the radially outer portion of the nozzlemount to the bearing housing. Accordingly, it is possible to reduce heatloss due to heat release from the radially outer portion of the nozzlemount to the bearing housing, and improve the turbine efficiency and theperformance of the turbocharger.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

(12) In some embodiments, in the above variable geometry turbocharger(10) or (11), the heat shield member has a lower thermal conductivitythan each of a thermal conductivity of the bearing housing and a thermalconductivity of the nozzle mount.

According to the above variable geometry turbocharger (12), it ispossible to reduce the heat release amount from the radially outerportion of the nozzle mount to the bearing housing effectively.

(13) In some embodiments, in the variable geometry turbochargeraccording to any one of the above (10) to (12), the heat shield memberis formed of austenitic stainless steel or nickel-based alloy.

According to the above variable geometry turbocharger (13), it ispossible to reduce the heat release amount from the radially outerportion of the nozzle mount to the bearing housing effectively, whileensuring the heat resistance performance of the heat shield memberitself.

(14) In some embodiments, in the variable geometry turbochargeraccording to any one of the above (10) to (13), the heat shield memberincludes a ring-shaped heat-shield plate disposed so that thebearing-housing side support portion and the nozzle mount do not makecontact with each other over an entire angular range in acircumferential direction of the turbine rotor.

According to the above variable geometry turbocharger (14), it ispossible to reduce the heat release amount from the radially outerportion of the nozzle mount to the bearing housing with a simpleconfiguration.

(15) In some embodiments, in the variable geometry turbochargeraccording to any one of the above (10) to (13), the heat shield memberincludes a coating applied to the radially outer portion of thebearing-housing side support portion or the nozzle mount.

According to the above variable geometry turbocharger (15), it ispossible to reduce the heat release amount from the radially outerportion of the nozzle mount to the bearing housing with a simpleconfiguration.

Advantageous Effects

According to at least one embodiment of the present invention, providedis a variable geometry turbocharger whereby it is possible to reduceheat loss due to heat release from the radially outer portion of thenozzle mount to the bearing-housing side support portion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a variable geometryturbocharger 100 according to an embodiment of the present invention,taken along the rotational axis O of the turbocharger 100.

FIG. 2 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100A) according to an embodiment.

FIG. 3 is a perspective view of a bearing housing 10 of the variablegeometry turbocharger 100 (100A) depicted in FIG. 2.

FIG. 4 is a schematic diagram showing positions of a bearing-housingside recess portion 46 and a bolt 44 with respect to the circumferentialdirection.

FIG. 5 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100B) according to an embodiment.

FIG. 6 is a diagram showing a relationship between a temporal change ofthe temperature of exhaust gas flowing through the scroll flow passage 4(004) and a temporal change of the heat release amount (passage heatamount) from the radially outer portion 38 (038) of the nozzle mount(016) to the bearing-housing side support portion 40 (040), for each ofthe variable geometry turbocharger 200 according to a comparativeembodiment shown in FIG. 13, the variable geometry turbocharger 100(100A) shown in FIG. 2, and the variable geometry turbocharger 100(100B) shown in FIG. 5.

FIG. 7 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100C) according to an embodiment.

FIG. 8 is a schematic perspective view showing a configuration exampleof a heat shield member 60.

FIG. 9 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100D) according to an embodiment.

FIG. 10 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100E) according to an embodiment.

FIG. 11 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100F) according to an embodiment.

FIG. 12 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 100 (100G) according to an embodiment.

FIG. 13 is a schematic enlarged cross-sectional view of a variablegeometry turbocharger 200 according to a comparative embodiment.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. It is intended, however,that unless particularly identified, dimensions, materials, shapes,relative positions and the like of components described in theembodiments shall be interpreted as illustrative only and not intendedto limit the scope of the present invention.

For instance, an expression of relative or absolute arrangement such as“in a direction”, “along a direction”, “parallel”, “orthogonal”,“centered”, “concentric” and “coaxial” shall not be construed asindicating only the arrangement in a strict literal sense, but alsoincludes a state where the arrangement is relatively displaced by atolerance, or by an angle or a distance whereby it is possible toachieve the same function.

For instance, an expression of an equal state such as “same” “equal” and“uniform” shall not be construed as indicating only the state in whichthe feature is strictly equal, but also includes a state in which thereis a tolerance or a difference that can still achieve the same function.

Further, for instance, an expression of a shape such as a rectangularshape or a cylindrical shape shall not be construed as only thegeometrically strict shape, but also includes a shape with unevenness orchamfered corners within the range in which the same effect can beachieved.

On the other hand, an expression such as “comprise”, “include”, “have”,“contain” and “constitute” are not intended to be exclusive of othercomponents.

FIG. 1 is a schematic cross-sectional view of a variable geometryturbocharger 100 according to an embodiment of the present invention,taken along the rotational axis O of the turbocharger 100.

The variable geometry turbocharger 100 includes a turbine rotor 2disposed coaxially with a non-depicted compressor, a turbine housing 6that houses the turbine rotor 2 and forms a scroll flow passage 4 on theradially outer side of the turbine rotor 2, a bearing housing 10 housinga bearing 8 supporting the turbine rotor 2 rotatably and being coupledto the turbine housing 6, and a variable nozzle mechanism 12 disposedbetween the turbine housing 6 and the bearing housing 10, for adjustingthe flow of exhaust gas from the scroll flow passage 4 to the turbinerotor 2.

Hereinafter, unless otherwise stated, the axial direction of the turbinerotor 2 is referred to as merely “axial direction”, and the radialdirection of the turbine rotor 2 is referred to as merely “radialdirection”, and the circumferential direction of the turbine rotor 2 isreferred to as merely “circumferential direction”.

The variable nozzle mechanism 12 includes a plurality of nozzle vanes14, a nozzle mount 16, a nozzle plate 18, a plurality of lever plates20, a drive ring 22, and a plurality of nozzle supports 24.

The plurality of nozzle vanes 14 are disposed at intervals in thecircumferential direction, in an exhaust gas flow passage 26 having anannular shape for introducing exhaust gas from the scroll flow passage 4to the turbine rotor 2.

The nozzle mount 16 is an annular plate disposed on the radially outerside of the turbine rotor 2, and forms a flow passage wall 28 on theside of the bearing housing 10, of the exhaust gas flow passage 26. Thenozzle mount 16 is provided with a plurality of support holes 30(through holes) for rotatably supporting the respective shaft portions15 of the plurality of nozzle vanes 14.

The nozzle plate 18 is an annular plate disposed on the radially outerside of the turbine rotor 2 so as to face the nozzle mount 16, and formsa flow passage wall 32 on the opposite side to the bearing housing 10,of the exhaust gas flow passage 26. Further, the nozzle plate 18 forms,on the downstream side of the flow passage wall 32, a shroud wall 34facing the tip-side ends of the blades of the turbine rotor 2 via a gap.The nozzle mount 16 and the nozzle plate 18 are coupled by a pluralityof nozzle supports 24.

A back plate 23 is disposed between the back face of the turbine rotor 2and the bearing housing 10, so that exhaust gas flowing from the exhaustgas flow passage 26 to the turbine rotor 2 does not leak toward the backside of the nozzle mount 16 (opposite to the exhaust gas flow passage26) through the radially inner side of the nozzle mount 16. The backplate 23 is in contact with the nozzle mount 16 at one end side in theaxial direction, and is in contact with the bearing housing 10 at theother end side in the axial direction.

In the variable nozzle mechanism 12 described above, the drive ring 22is rotary driven by a driving force transmitted from a non-depictedactuator. When the drive ring 22 rotates, the lever plates 20 being inengagement with the drive ring 22 rotate the shaft portions 15 of thenozzle vanes 14, and as a result, the nozzle vanes 14 rotate to changethe vane angle of the nozzle vanes 14, thereby adjusting the flow ofexhaust gas from the scroll flow passage 4 to the turbine rotor 2.

In the depicted embodiment, an annular space 36 housing the lever plate20 and the drive ring 22 is formed between the bearing housing 10 andthe nozzle mount 16.

The bearing housing 10 includes a bearing-housing side support portion40 having an annular shape and supporting the radially outer portion 38of the nozzle mount 16 from the opposite side to the scroll flow passage4 in the axial direction of the turbine rotor 2. The bearing-housingside support portion 40 is formed on the radially outer side of theannular space 36. On the radially outer side of the bearing-housing sidesupport portion 40, a seal ring 41 is disposed between the turbinehousing 6 and the bearing housing, and the seal ring 41 prevents leakageof exhaust gas from between the bearing housing 10 and the turbinehousing 6.

The turbine housing 6 includes a turbine-housing side support portion 42having an annular shape and supporting the radially outer portion 38 ofthe nozzle mount 16 from the opposite side to the bearing-housing sidesupport portion 40 in the axial direction.

The nozzle mount 16 is held between the bearing-housing side supportportion 40 and the turbine-housing side support portion 42. In thedepicted embodiment, the turbine housing 6 and the bearing housing 10are fastened in the axial direction by a plurality of bolts 44 disposedat intervals in the circumferential direction, and the nozzle mount 16is held between the bearing-housing side support portion 40 and theturbine-housing side support portion 42 by the axial force of the bolts44.

FIG. 2 is a schematic enlarged cross-sectional view of a configurationexample 100 (100A) of a variable geometry turbocharger 100 (100A). FIG.3 is a perspective view of a bearing housing 10 of the variable geometryturbocharger 100 (100A) depicted in FIG. 2.

In an embodiment, as shown in FIGS. 2 and 3, the bearing-housing sidesupport portion 40 includes at least one bearing-housing side recessportion 46 formed so as to be recessed opposite to the nozzle mount 16in the axial direction. In the depicted embodiment, the bearing-housingside support portion 40 includes a plurality of bearing-housing siderecess portions 46 disposed at intervals in the circumferentialdirection.

According to the above configuration, with the bearing-housing siderecess portions 46, it is possible to reduce the contact area betweenthe bearing-housing side support portion 40 and the radially outerportion 38 of the nozzle mount 16, and to reduce the heat release amountfrom the radially outer portion 38 of the nozzle mount 16 to the bearinghousing 10, through the heat insulating effect of an air layer 39between the bearing-housing side recess portion 46 and the radiallyouter portion 38 of the nozzle mount 16. Accordingly, it is possible toreduce heat loss due to heat release from the radially outer portion 38of the nozzle mount 16 to the bearing housing 10, and improve theturbine efficiency and the performance of the turbocharger 100.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

FIG. 4 is a schematic diagram showing positions of a bearing-housingside recess portion 46 and a bolt 44 with respect to the circumferentialdirection.

In an embodiment, as shown in FIG. 4, with respect to thecircumferential direction, each of the bearing-housing side recessportions 46 is formed in an angular range Ar that does not overlap withthe center position Pv of a bolt 44 adjacent to the bearing-housing siderecess portion 46, of the plurality of bolts 44.

Accordingly, for the center position Pv and the angular range Ar do notoverlap with each other, it is possible to reduce heat loss due to heatrelease from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10 while ensuring a fastening force between the bearinghousing 10 and the turbine housing 6 achieved by the bolts 44.

In an embodiment, as shown in FIG. 4, each of the bearing-housing siderecess portions 46 is five degrees or more apart from the centerposition of the bolt 44 adjacent to the bearing-housing side recessportion 46, of the plurality of bolts 44. That is, the angle α shown inFIG. 4 is not smaller than five degrees.

Accordingly, it is possible to reduce heat loss due to heat release fromthe radially outer portion 38 of the nozzle mount 16 to the bearinghousing 10 while ensuring a strong fastening force between the bearinghousing 10 and the turbine housing 6 achieved by the bolts 44.

FIG. 5 is a schematic enlarged cross-sectional view of a configurationexample 100 (100B) of a variable geometry turbocharger 100.

In an embodiment, as shown in FIG. 5, the turbine-housing side supportportion 42 is disposed so as to protrude inward in the radial directionfrom the bearing-housing side support portion 40 along the surface 48 ofthe radially outer portion 38 of the nozzle mount 16 (surface on theside of the scroll flow passage 4). That is, the radially inner end 54of the turbine-housing side support portion 42 is positioned on theinner side of the radially inner end 59 of the bearing-housing sidesupport portion 40 with respect to the radial direction.

Typically, as shown in FIG. 13, to nip the nozzle mount 016 with asimple structure, the radially inner end 054 of the turbine-housing sidesupport portion 42 is positioned on the same position as the radiallyinner end 059 of the bearing-housing side support portion 040 withrespect to the radial direction.

In contrast, in the configuration shown in FIG. 5, the turbine-housingside support portion 42 is disposed so as to protrude inward in theradial direction from the bearing-housing side support portion 40 alongthe surface 48 of the nozzle mount 16, and thus it is possible toincrease the area of the nozzle mount 16 covered with theturbine-housing side support portion 42 compared to that in a typicalstructure shown in FIG. 13. Thus, it is possible to reduce the area of aportion of the nozzle mount 16 exposed to a high-temperature exhaust gasflow from the scroll flow passage 4 to the exhaust gas flow passage 26(heat transfer area). Accordingly, the heat absorption amount of thenozzle mount 16 reduces, and thus an increase in the metal temperatureof the nozzle mount 16 is suppressed. Accordingly, the temperaturedifference between the nozzle mount 16 and the bearing housing 10becomes small, and thus it is possible to reduce heat loss due to heatrelease from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10, and improve the turbine efficiency and theperformance of the turbocharger 100.

Further, it is possible to suppress a decrease in the exhaust gastemperature of the turbine outlet side. Thus, in a case where a catalystfor purifying exhaust gas is disposed on the downstream side of theturbine, it is possible to suppress performance deterioration of thecatalyst due to the temperature decrease of the catalyst, and reducecontent of impurity substances (e.g. NOx and SOx) in the exhaust gas.

In an embodiment, as shown in FIG. 5, the turbine-housing side supportportion 42 includes a contact portion 50 being in contact with theradially outer portion 38 of the nozzle mount 16 and a non-contactportion 52 formed on the inner side of the contact portion 50 withrespect to the radial direction and facing the nozzle mount 16 via a gapg. In the depicted embodiment, the non-contact portion 52 includes astep formed from the contact portion 50 so as to provide the gap gbetween the non-contact portion 52 and the nozzle mount 16.

With the above configuration, the turbine-housing side support portion42 has the non-contact portion 52 on the inner side of the contactportion 50 with respect to the radial direction, and thus it is possibleto cover the radially outer portion 38 of the nozzle mount 16 with theturbine-housing side support portion 42 while suppressing an increase inthe contact area between the bearing-housing side support portion 40 andthe radially outer portion 38 of the nozzle mount 16. Accordingly, it ispossible to reduce the area of a portion of the nozzle mount 16 exposedto a high-temperature exhaust gas flow from the scroll flow passage 4 tothe exhaust gas flow passage 26 (heat transfer area), and suppress anincrease in the heat input amount to the radially outer portion 38 ofthe nozzle mount 16 from the turbine-housing side support portion 42.Accordingly, it is possible to suppress an increase in the metaltemperature of the nozzle mount 16 effectively, and reduce heat loss dueto heat release from the radially outer portion 38 of the nozzle mount16 to the bearing housing 10 effectively.

In an embodiment, as shown in FIG. 5, an expression0≤(r1−r3)/(r2−r3)≤0.75 is satisfied, where r1 is the distance betweenthe radially inner end 54 of the turbine-housing side support portion 42and the rotational axis O of the turbine rotor 2, r2 is the distancebetween the radially outer end 64 of the nozzle mount 16 and therotational axis O, and r3 is the distance between the radially outer endof the nozzle mount and the rotational axis. In the depicted embodiment,an expression 0≤(r1−r3)/(r2−r3)≤0.30 is satisfied.

With the above configuration, it is possible to suppress an increase inthe metal temperature of the nozzle mount 16 effectively, and reduceheat loss due to heat release from the radially outer portion 38 of thenozzle mount 16 to the bearing housing 10 effectively, withoutinterfering a smooth flow in the exhaust gas flow passage 26 between thenozzle mount 16 and the nozzle plate 18.

Further, the bearing housing 10 in the embodiment depicted in FIG. 5 hasthe same configuration as the bearing housing 10 in the embodimentdepicted in FIGS. 2 and 3, and thus the same reference numerals are usedto avoid repeating the same description.

FIG. 6 is a diagram showing a relationship between a temporal change ofthe temperature of exhaust gas flowing through the scroll flow passage 4(004) and a temporal change of the heat release amount (passage heatamount) from the radially outer portion 38 (038) of the nozzle mount(016) to the bearing-housing side support portion 40 (040), for each ofthe variable geometry turbocharger 200 according to a comparativeembodiment shown in FIG. 13, the variable geometry turbocharger 100(100A) shown in FIG. 2, and the variable geometry turbocharger 100(100B) shown in FIG. 5. In FIG. 6, the solid line indicates the temporalchange of the exhaust gas temperature that is common in the respectiveembodiments, while the dotted line indicates the temporal change of theheat release amount in the variable geometry turbocharger 200 accordingto a comparative embodiment. Further, the single-dotted chain lineindicates the temporal change of the heat release amount in the variablegeometry turbocharger 100 (100A), while the double-dotted chain lineindicates the temporal change of the heat release amount in the variablegeometry turbocharger 100 (100B).

As shown in FIG. 6, with the variable geometry turbocharger 100 (100A)depicted in FIG. 2, it is possible to reduce the heat release amount(heat passage amount) from the radially outer portion 38 (038) of thenozzle mount (016) to the bearing-housing side support portion 40 (040),compared to the variable geometry turbocharger 200 according to thecomparative embodiment. According to estimation of the presentinventors, with the variable geometry turbocharger 100 (100A), it ispossible to reduce heat loss by approximately 47% compared to thevariable geometry turbocharger 200.

Furthermore, as shown in FIG. 6, with the variable geometry turbocharger100 (100B) depicted in FIG. 5, it is possible to reduce the heat releaseamount (heat passage amount) from the radially outer portion 38 (038) ofthe nozzle mount (016) to the bearing-housing side support portion 40(040), compared to the variable geometry turbocharger 200 according tothe comparative embodiment. According to estimation of the presentinventors, with the variable geometry turbocharger 100 (100B), it ispossible to reduce heat loss by approximately 57% compared to thevariable geometry turbocharger 200.

FIG. 7 is a schematic enlarged cross-sectional view of a configurationexample 100 (100C) of the variable geometry turbocharger 100.

In an embodiment, as shown in FIG. 7, a heat shield member 60 isdisposed between the bearing-housing side support portion 40 and thenozzle mount 16.

With the above configuration, through the heat shield effect of the heatshield member 60, it is possible to reduce the heat release amount fromthe radially outer portion 38 of the nozzle mount 16 to the bearinghousing 10. Accordingly, it is possible to reduce heat loss due to heatrelease from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10, and improve the turbine efficiency and theperformance of the turbocharger 100. Further, it is possible to suppressa decrease in the exhaust gas temperature of the turbine outlet side.Thus, in a case where a catalyst for purifying exhaust gas is disposedon the downstream side of the turbine, it is possible to suppressperformance deterioration of the catalyst due to the temperaturedecrease of the catalyst, and reduce content of impurity substances(e.g. NOx and SOx) in the exhaust gas.

In an embodiment, in the variable geometry turbocharger 100 (100C)depicted in FIG. 7, the thermal conductivity of the heat shield member60 is smaller than each of the thermal conductivity of the bearinghousing 10 and the thermal conductivity of the nozzle mount 16.

With the above configuration, it is possible to reduce the heat releaseamount from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10 effectively.

In an embodiment, in the variable geometry turbocharger 100 (100C)depicted in FIG. 7, the heat shield member 60 is formed of austeniticstainless steel or nickel-based alloy. It is preferable to use anaustenitic stainless steel other than SUS 304, for example,Cr-10Ni-6Mn-1Mo for boiler tubes. As a nickel-based alloy, the followingcan be used suitably: Incoloy 800 (Ni-45Fe-21Cr-0.4Ti), Inconel 600(Ni-16Cr-6Fe), Inconel X-750 (Ni-15Cr-7Fe-2.5Ti-0.6Al-0.8Nb), HastelloyC (Ni-16Mo-15Cr-4W-5Fe), or Nimonic 90 (Ni-20Cr-17Co-2.4Ti-1.4Al).Further, the heat shield member 60 may be formed of 25Cr-20Ni anti-heatcast steel (equivalent to SUS 310) and 35Ni-15Cr anti-heat cast steel(equivalent to SUS 330). It should be noted that Incoloy, Inconel,Hastelloy, and Nimonic are trademarks.

With the above configuration, it is possible to reduce the heat releaseamount from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10 effectively, while ensuring the heat resistanceperformance of the heat shield member 60 itself.

In an embodiment, in the variable geometry turbocharger 100 (100C)depicted in FIG. 7, the heat shield member 60 may be a ring-shaped heatshield plate (see FIG. 8) disposed so that the bearing-housing sidesupport portion 40 and the nozzle mount 16 do not make contact with eachother over the entire angular range in the circumferential direction.

With the above configuration, it is possible to reduce the heat releaseamount from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10 through a simple configuration.

In an embodiment, in the variable geometry turbocharger 100 (100C)depicted in FIG. 7, the heat shield member 60 may be a coating appliedto the radially outer portion 38 of the nozzle mount 16 or the bearinghousing 10 so that the bearing-housing side support portion 40 and thenozzle mount 16 do not make contact with each other over the entireangular range in the circumferential direction.

With the above configuration, it is possible to reduce the heat releaseamount from the radially outer portion 38 of the nozzle mount 16 to thebearing housing 10 through a simple configuration.

Embodiments of the present invention were described in detail above, butthe present invention is not limited thereto, and various amendments andmodifications may be implemented.

For instance, in the variable geometry turbocharger 100 (100A) describedwith reference to FIGS. 2 to 4, the bearing-housing side support portion40 includes a bearing-housing side recess portion 46 formed so as to berecessed opposite to the nozzle mount 16. Nevertheless, the presentinvention is not limited to the above embodiment, and as depicted inFIG. 9 for instance, the radially outer portion 38 of the nozzle mount16 may include at least one nozzle-mount side recess portion 62 formedso as to be recessed opposite to the bearing housing 10 in the axialdirection.

Also with the above configuration, with the nozzle-mount side recessportions 62, it is possible to reduce the contact area between thebearing-housing side support portion 40 and the radially outer portion38 of the nozzle mount 16, and to reduce the heat release amount fromthe radially outer portion 38 of the nozzle mount 16 to the bearinghousing 10, through the heat insulating effect of the air layer 39between the nozzle-mount side recess portion 62 and the bearing-housingside support portion 40. Accordingly, it is possible to reduce heat lossdue to heat release from the radially outer portion 38 of the nozzlemount 16 to the bearing housing 10, and improve the turbine efficiencyand the performance of the turbocharger 100. Furthermore, the preferablearrangement of the nozzle-mount side recess portion 62 in thecircumferential direction is similar to the preferable arrangement ofthe bearing-housing side recess portion 46 in the circumferentialdirection described above with reference to FIGS. 3 and 4.

Further, in the embodiment shown in FIGS. 2 and 3, the bearing-housingside recess portion 46 is formed from the radially inner side to theradially outer side of the bearing-housing side support portion 40.Nevertheless, the formation range of the bearing-housing side recessportion 46 in the radial direction is not limited this. For instance,the bearing-housing side recess portion 46 may be formed only on theradially inner side of the bearing-housing side support portion 40 asdepicted in FIG. 10, only on the radially outer side of thebearing-housing side support portion 40 as depicted in FIG. 11, or onlyin the center of the bearing-housing side support portion 40 withrespect to the radial direction. Furthermore, also in the embodimentshown in FIGS. 10 to 12, the preferable arrangement of thebearing-housing side recess portion 46 in the circumferential directionis similar to the preferable arrangement of the bearing-housing siderecess portion 46 described above with reference to FIGS. 3 and 4.Further, the respective embodiments depicted in FIGS. 9 to 12 can beapplied to the respective embodiments described with reference to FIGS.1 to 8.

DESCRIPTION OF REFERENCE NUMERALS

-   2 Turbine rotor-   4 Scroll flow passage-   6 Turbine housing-   8 Bearing-   10 Bearing housing-   12 Variable nozzle mechanism-   14 Nozzle vane-   15 Shaft portion-   16 Nozzle mount-   18 Nozzle plate-   20 Lever plate-   22 Drive ring-   23 Back plate-   24 Nozzle support-   26 Exhaust gas flow passage-   28 Flow passage wall-   30 Support hole-   32 Flow passage wall-   34 Shroud wall-   36 Annular space-   38 Radially outer portion-   39 Air layer-   40 Bearing-housing side support portion-   41 Seal ring-   42 Turbine-housing side support portion-   44 Bolt-   46 Bearing-housing side recess portion-   48 Surface-   50 Contact portion-   52 Non-contact portion-   54 Radially inner end-   59 Radially inner end-   60 Heat shield member-   62 Nozzle-mount side recess portion-   64 Radially outer end-   100 (100A to 199G) Variable geometry turbocharger-   200 Variable geometry turbocharger-   Ar Angular range-   H Arrow-   O Rotational axis-   Pv Center position-   g Gap

1. A variable geometry turbocharger, comprising: a turbine rotor; aturbine housing which accommodates the turbine rotor and which forms atleast a part of a scroll flow passage through which exhaust gas to besupplied to the turbine rotor flows: a bearing housing accommodating abearing which rotatably supports the turbine rotor, the bearing housingbeing coupled to the turbine housing; and a variable nozzle mechanismfor adjusting a flow of exhaust gas to the turbine rotor from the scrollflow passage formed on a radially outer side of the turbine rotor,wherein the variable nozzle mechanism includes: a nozzle vane disposedin an exhaust gas flow passage for guiding the exhaust gas from thescroll flow passage to the turbine rotor; a nozzle mount having anannular shape and supporting the nozzle vane rotatably, the nozzle mountforming a flow passage wall on a bearing-housing side of the exhaust gasflow passage; and a nozzle plate having an annular shape and beingdisposed so as to face the nozzle mount, the nozzle plate forming a flowpassage wall on a side opposite to the bearing housing, of the exhaustgas flow passage, wherein the bearing housing includes a bearing-housingside support portion configured to support a radially outer portion ofthe nozzle mount from a side opposite to the scroll flow passage in anaxial direction of the turbine rotor, wherein the turbine housingincludes a turbine-housing side support portion configured to supportthe radially outer portion of the nozzle mount from a side opposite tothe bearing-housing side support portion in the axial direction, whereinthe nozzle mount is nipped by the turbine-housing side support portionand the bearing-housing side support portion, and wherein theturbine-housing side support portion is disposed so as to protrudetoward an inner side of the bearing-housing side support portion in aradial direction of the turbine rotor, along a surface of the nozzlemount.